1. Field of the Invention
The present invention relates to a steering control system for use in a moving vehicle, and more particularly to a steering control system for use in a moving vehicle such as a moving automobile, an unmanned mobile and carrying device in a factory, or an automated vehicle for use in agriculture, civil engineering machinery and the like.
2. Description of the Prior Art
Heretofore, as a system for detecting a current position of a moving body such as the moving vehicles described above, there has been proposed a system provided with a means for scanning a light beam emitted from a beam source on a moving body in the circumferential direction or every azimuthal directions around the moving body, retro-reflective means for reflecting to return the light beam in the direction of incident light which are secured at at least three positions apart from the moving body, and a beam receiver means for receiving light reflected from the retroreflective means (Japanese Patent Laid-open No. 67476/1984).
In the above mentioned prior art, differential azimuths between adjoining two of the at least three retroreflective means around the moving body, or included angles formed by the adjoining two of said at least three retroreflective means with the moving body are detected on the basis of received beam outputs of the light-receiving means, and then the position of the moving body is calculated on the basis of the detected differential azimuths and positional information of the retroreflective means which have been previously set.
In the above described system, however, there has been such a case where a light beam emitted from a beam source mounted on the moving vehicle could not be directed to the retroreflective means positioned at reference points because of an inclination or vibration of the moving vehicle, or a case where the light-receiving means on the moving vehicle receives light reflected from the objects other than the expected retroreflective means.
When real reflected light is not positively received by a light-receiving means, the position of the moving vehicle is erroneously calculated so that the moving vehicle cannot be traveled along a prescribed course.
To solve the problem mentioned above, there has been proposed a system in which a light beam is scanned in the circumferential direction around a moving vehicle while it is vertically swung, whereby the light beam can move reliably be irradiated to a predetermined light reflecting means even if the moving vehicle inclines (Japanese Patent Publication No. 41489/1988).
In addition, there is a light beam scanning system in which a plurality of light beams are simultaneously scanned in the different circumferential directions corresponding to the individual light reflecting means by a plurality of light beam scanning devices which can freely swing the plurality light in the vertical directions, whereby the missing of the light reflecting means is made as little as possible (Japanese Patent Application Laid-Open No. 242313/1985).
In the former system, if the scanning speed in the circumferential direction is high as compared with the swing speed in the vertical directions, the pitch of the locus of the light beam in the circumferential scanning direction becomes rough. That is, the locus of the light beam in this system is a periodic wave-like locus which is a composite of the circumferential scanning and the vertical scanning or swing; therefore, the wavelength of the wave-like locus becomes long if the circumferential scanning speed is high as compared with the vertical swing speed. Moreover, if the light reflecting means happens to be positioned between two locus lines adjoining each other, the light beam cannot be irradiated on a predetermined light reflecting means. The vertical scanning density of the light beam can be enhanced by reducing the circumferential scanning speed, but there is a problem that the amount the moving vehicle moves during a one-rotation scanning time increases for that reduction and the precision of detecting the position of the moving vehicle decreases.
In the latter system, although the problem of the circumferential scanning speed is somewhat improved, it is required to provide a plurality of light beam scanning means, which causes another problem, i.e., the signal processing therefor is complex and the system also becomes expensive.
Because of such actual circumstances it is extremely difficult to prevent the missing of a predetermined light reflecting means or object to be detected, and it is often required to accurately recognize that the missing of a reference point has occurred and to appropriately treat for the missing. The present applicant has proposed several reference point discrimination processing methods for determining whether the predetermined light reflecting means or object can be detected or it has been missed.
There is the following method as an example of such reference point discriminating processing methods. That is, based on the azimuth of the light reflecting means detected up to the present time, the azimuth in which the same light reflecting means is to be detected in the next scan is predicted, and if there is a light signal received in the predicted azimuth, the detected azimuth of the received light signal is assumed to be the azimuth in which the predetermined light reflecting means exists, and the detected azimuth is used for the steering control of the moving vehicle. On the other hand, if no light signal is detected in the predicted azimuth, said light reflecting means is judged to have been missed. Then the predicted azimuth is assumed to be the azimuth of the missing light reflecting means, and it is used for the steering control.
In the above reference point discrimination process, the disposed light reflecting means are sequentially discriminated in the rotation direction by the rotary scanning of one light beam. For that, it is necessary to recognize the azimuths of all the predetermined light reflecting means prior to the running of the vehicle.
However, in the above-mentioned system in which a light beam is scanned in the circumferential direction while it is vertically swung, even if it is desired to recognize the azimuth of each light reflecting means prior to the running of the moving vehicle, the light beam cannot be irradiated on the light reflecting means when the light reflecting means is positioned between the two adjoining wave-like scanning locus lines of the light beam, and thus the light reception sequence is different from the sequence in which the light reflecting means are actually disposed, so that the respective light reflecting means cannot correspond to the azimuths measured.